1. Field of the Invention
This invention relates to a circuit for driving an ink jet type recording head in which a vibrating board forming a pressure chamber is displaced with a bar-shaped piezo-electric vibrator, so that the pressure chamber is compressed to jet ink droplets through nozzle openings (hereinafter referred to as "an ink jet type recording head driving circuit").
2. Description of the Prior Art
An ink jet type recording head for a recording apparatus is well know in the art which is so designed that, as disclosed for instance by Japanese Patent Application Publication No. 24218/1990, a disk-shaped piezo-electric vibrating plate is secured to an elastic board forming a pressure chamber. In the ink jet type recording head of this type, the displacement of the piezo-electric vibrator is small, and therefore it is essential that the pressure chamber is large in effective area. Therefore, in the recording head, the pressure chamber is located relatively far from the nozzle openings, and it is communicated with the latter through ink passageways. Hence, the recording head is unavoidably bulky. In addition, delicate adjustment is required for making the ink passageways uniform in fluid resistance.
In order to eliminate the above-described difficulties, for instance U.S. Pat. No. 4,697,193 has disclosed an ink jet type recording head in which a bar-shaped piezo-electric vibrator is abutted against a vibrating board forming a pressure chamber so as to compress and release the latter, so that ink droplets are formed by the longitudinal vibration of the piezo-electric vibrator.
The ink jet type recording head operating on the above-described longitudinal vibration employs a so-called "draw and strike" type driving system that, immediately before formation of a dot, a driving voltage is applied to the piezo-electric vibrator to contract the latter, and then the piezo-electric vibrator is discharged so that it is stretched to compress the pressure chamber thereby to form an ink droplet.
Employment of the "draw and strike" type driving system is advantageous in that the elastic energy stored in the piezo-electric vibrator or vibrating board in advance can be utilized, and in addition the ink can be positively led into the pressure chamber. However, it is disadvantageous in that, if the operating frequency of the piezo-electric vibrator is increased to increase the printing speed, then in formation of an ink droplet the meniscus of ink in the vicinity of the nozzle fluctuates in position, so that the ink droplet formed is changed in the velocity of flight and in size, and therefore the resultant print is low in quality.
In order to overcome the above-described difficulty, a driving method has been proposed in which the piezo-electric vibrator contracted is kept as it is until the meniscus returns to the original position and stops there, and thereafter the piezo-electric vibrator is stretched by discharging it. However, the driving system is still disadvantageous in that there is a wait time for restoration of the meniscus, which limits the printing speed.
The characteristic of printing with respect to temperature of the ink jet type recording head is liable to change when compared with those of other type recording heads such as a wire dot type recording head and a thermal transfer type recording head. Hence, the ink jet type recording head employs a temperature compensating circuit so that the driving voltage is controlled according to a detection signal provided by a temperature sensor. Accordingly, in this case, it is necessary to provide a power source circuit for driving the ink jet type recording head in addition to a power source circuit for a pulse motor or the like adapted to drive the printing mechanism; that is, the resultant printing machine is intricate in construction as much.
The piezo-electric vibrator of longitudinal vibration mode, being small in section, is advantageous in that a plurality of such piezo-electric vibrators can be readily arranged with high density. However, it is disadvantageous in that the piezo-electric vibrators arranged adjacent to one another suffer from mutual interference, which lowers the quality of the resultant print.